Search results for: 7Sep
#22963332 
2012/09/10
To Up
Synthesis and characterization of hypoelectronic tantalaboranes: comparison of the geometric and electronic structures of [(Cp*TaX)2B5H11] (X = Cl, Br, and I).
Mild thermolysis of tantalaborane [(Cp*Ta)(2)B(5)H(11)], 1 (Cp* = η(5)-C(5)Me(5)) in presence of halogen sources affords the open cage clusters [(Cp*TaX)(2)B(5)H(11)], 2-4 (2: X = Cl; 3: X = Br; and 4: X = I) in good yields. In contrast, the tetraborohydride cluster, [(Cp*Ta)(2)B(4)H(9)(μ-BH(4))], 5, under the same reaction conditions forms the B-H substituted cluster [(Cp*Ta)(2)B(4)H(8)I(μ-BH(4))], 6. All the new metallaboranes have been characterized by mass spectrometry, (1)H, (11)B, (13)C NMR spectroscopy, and elemental analysis, and the structural types were established by crystallographic analysis of clusters 3, 4, and 6. Density functional theory (DFT) calculations at the BP86/TZ2P ZORA level reveal geometries in agreement with the structure determinations, large gaps between the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) in accord with their stabilities. B3LYP-computed (11)B chemical shifts accurately reflect the experimentally measured shifts. Clusters 2-4 can be viewed as 7-sep 7-vertex oblatoarachno M(2)B(5) clusters which can be generated from a 7-sep 9-vertex oblatocloso M(2)B(7) cluster by removal of two equatorial boron atoms. Cluster 6 can be considered as an electron-deficient 6-sep 6-vertex oblatoarachno M(2)B(4) cluster derived from an 8-vertex oblatocloso hexagonal bipyramidal cluster, in which BH(4)(-) anion is weakly bonded in a bidentate mode.K Geetharani, Bellie Sundaram Krishnamoorthy, Samia Kahlal, Shaikh M Mobin, Jean-François Halet, Sundargopal Ghosh
2499 related Products with: Synthesis and characterization of hypoelectronic tantalaboranes: comparison of the geometric and electronic structures of [(Cp*TaX)2B5H11] (X = Cl, Br, and I).
1 ml10 mg100 mg100ug200ul25 mg100 mg 5 G 25 MG2.5 mg100ul10 mg
Related Pathways
#11154594 //
To Up
Role of the transition metal in metallaborane chemistry. Reactivity of (Cp*ReH2)2B4H4 with BH3.thf, CO, and Co2(CO)8.
The reaction of Cp*ReCl4, [Cp*ReCl3]2, or [Cp*ReCl2]2 (Cp* = eta 5-C5Me5) with LiBH4 leads to the formation of 7-skeletal-electron-pair (7-sep) (Cp*ReH2)2(B2H3)2 (1) together with Cp*ReH6. Compound 1 is metastable and eliminates H2 at room temperature to generate 6-sep (Cp*ReH2)2B4H4 (2). The reaction of 2 with BH3.thf produces 7-sep (Cp*Re)2B7H7, a hypoelectronic cluster characterized previously. Heating of 2 with 1 atm of CO leads to 6-sep (Cp*ReCO)(Cp*ReH2)B4H4 (3). Both 2 and 3 have the same bicapped Re2B2 tetrahedral cluster core structure. Monitoring the reaction of 2 with CO at room temperature by NMR reveals the formation of a 7-sep, metastable intermediate, (Cp*ReCO)(Cp*ReH2)(B2H3)2 (4), which converts to 3 on heating. An X-ray structure determination reveals two isomeric forms (4-cis and 4-trans) in the crystallographic asymmetric unit which differ in geometry relative to the disposition of the metal ancillary ligands with respect to the Re-Re bond. The presence of these isomers in solution is corroborated by the solution NMR data and the infrared spectrum. In both isomers, the metallaborane core consists of fused B2Re2 tetrahedra sharing the Re2 fragment. On the basis of similarities in electron count and spectroscopic data, 1 also possesses the same bitetrahedral structure. The reaction of 2 with CO2(CO)8 results in the formal replacement of the four rhenium hydrides with a 4-electron CO2(CO)5 fragment, thereby closing the open face in 2 to produce the 6-sep hypoelectronic cluster (Cp*Re)2CO2(CO)5B4H4 (5). These reaction outcomes are compared and contrasted with those previously observed for 5-sep (Cp*Cr2)2B4H8.S Ghosh, X Lei, M Shang, T P Fehlner